In the past signals were derived from a large number of molecules making up a material on a so-called macro level, an example being the transistor. Now, according to the present invention, signals are derived from changes in state in a single molecule. These individual states can be read out or analyzed by vibrational spectroscopy techniques, for example, Raman spectroscopy techniques, or perhaps by other optical analysis techniques. In order to resolve the signal spatially and in intensity Raman spectroscopy is preferred.
Typical response times for conventional electrical devices, e.g. to accomplish a switching function, have been on the order of 10−9 or 10−10 second. Various techniques for still more quickly switching signals and information have been developed, such as the Josephson junction. A disadvantage to such fast-acting electrical switches or switch junctions has been the extreme temperature requirements. For example, a Josephson junction type of fast-acting electrical switch must be very cold, e.g. super cooled. Typically liquid helium is used to maintain the switching junction at the desired cold temperature for proper operation. The cost and space requirements to maintain such temperature conditions are counter-productive to the goals of cost reduction and miniaturization, which are highly sought in the computer field, for example.
As is demonstrated in U.S. Pat. No. 4,804,930, phthalocyanine molecules as molecular monomeric units or in general electrochemically semi-organized forms, can provide a variety of electro-optical properties. Fast switching effect, multilevel logic, memory states are experimentally well documented in the above patent and other publications.
As is disclosed in U.S. Pat. No. 4,04,930, the inventor has discovered that the observable changes in the electrical and optical characteristics of individual molecules caused by the electrical and/or optical excitation or de-excitation of electrons within such molecules can be used as signals which in turn can be used to carry information and that such observable information carrying changes or signals can be switched, amplified, and modulated by varying the optical as well as the electrical inputs to such molecules.
In the invention electro-optical molecules are adsorbed on a substrate. The natural characteristic of such a molecule is altered by ionization or electron transfer; more specifically an electron is excited to an excited state. Electron transfer, trapping, or excitation/state change, or molecule ionization is effected and controlled as a function of (1) electric potential across an adsorbed molecule or a layer or layers of such molecules and/or (2) wavelength(s)/frequency(ies) and intensity(ies) of the incident illumination thereof. Such electron transfer, trapping, or state change causes a change in the natural or non-perturbed optical response of the adsorbed molecule. Thus, state and state change as they are used herein refer to electron location within a molecule, energy level of such electron, and/or spin state of such electron. The optical response can be detected using Raman spectroscopy, preferably surface enhanced Raman spectroscopy. Such detection or analysis provides a spatial distribution of the Raman lines, each having a particular intensity or magnitude level. Analysis of the frequency or spatial distribution as well as the intensity of such output signal(s) or information identifies where such electron is trapped or transferred in the adsorbed molecule.
The frequency or spatial distribution of such output signal, therefore, is a function of the location in the molecule at which the electron is trapped or transferred; i.e. which electron has had a state change. Such state change or trapping may be referred to equivalently herein. Such trapping or electron excitation affects the natural vibrational characteristics of molecular bonds of the adsorbed molecule. Indeed, for example, in response to a particular electrical potential applied to adsorbed molecules and a particular optical input to such molecules, the natural vibrational state of one of the molecular bonds of such molecule may be altered to emit an optical or light output having a characteristic frequency or Raman spatial distribution that can be detected and analyzed and used for signaling or informational purposes. Using Raman spectroscopy input laser light of a given frequency will beat with the frequency of vibration of a particular band to cause re-emission of light from the molecule, and such re-emitted light or scattered light then has a spectral component that is related to such vibrational characteristic of the bond. Thus, excitation of an electron in a molecule to distort and, therefore, to change the vibrational character of a bond therein will affect the optical output from the molecule.
Since the invention takes advantage of light that is emitted in response to intramolecular electron excitation mechanisms, the response of the optical output signals is limited by the lifetimes of the vibrational excited states, for example on the order of about 2×10−13 second. Response times on the order of 10−15 second are expected to be observed for molecules that exhibit tunneling. Moreover, it has been discovered that such extremely fast response is achievable at typical room ambient temperatures without requiring super cooling, such as that needed for Josephson junction technology. Such response may be detected, e.g. by a light sensor, thereby to provide fast switching, read-out, etc. functions.
The invention may be used to obtain from the output light emitted by the molecule(s) one or more distinct output signals, each of which may be at different intensity levels. Such signals are distinguished from each other in the frequency or energy domain. Single or multiple signal outputs from the overall system is possible. The Raman spectrum line from a distinct frequency then would represent a specific output signal or information which could be used in multilevel fashion, such as multilevel logic, etc. The existence of such a line and the intensity thereof can be used as or can be used to derive output information that is based on intramolecular electron distribution within the said molecule. Thus, for example, for such multisignal output use, while maintaining a constant incident illumination of the adsorbed molecules, changing the applied potential may cause various ones of the Raman spectrum output lines to vary respectively in intensity; such variations need not necessarily be the same for each line. For single output, while maintaining a constant incident illumination of the adsorbed molecules, as will be described in greater detail below, variation of the potential across the adsorbed molecules can effect a modulation of the Raman signal. Conversely, a similar effect on the output may be achieved by changing the intensity and/or wavelength(s)/frequency(ies) of the incident illumination while maintaining constant the applied electric potential and incident illumination.
The invention envisions the realization that a molecular size device can be used to derive an output that can be treated as a signal for carrying information and such signals can be modulated at very high speeds. Exemplary speeds may be on the order of from about 10−13 to about 10−15 second. To accomplish that purpose the invention achieves an operative system by selecting a molecular species and means for applying thereto the electrical and optical inputs to obtain detectable outputs.
Preferred molecules would be macrocyclics, such as various metallated phthalocyanines, porphyrines, chlorophyls, hemes, or cytochromes. However, other molecules may be used according to the invention if they respond to the desired input to achieve an excited state that can produce a useful detectable output. For some applications of the invention the molecules, and preferably macrocyclics, should exhibit semiconductor properties.
To apply electric potential to or to obtain electric polarization of the molecules, the molecules should be adsorbed on a conducting or semiconducting substrate. Preferable conducting substrates would be, for example, silver, gold, platinum, palladium, silver bromide, silver iodide, copper, and aluminum, and halides of these metals; the most preferred would be silver and silver halides. Preferred doped or non-doped semiconductor substrates would be, for example, galium arsenide, tin oxide, zinc oxide, silver oxide, cadmium sulfate, germanium. Organic material exhibiting similar characteristics also may be used as the substrate that can provide charge transfer from higher energy states to the lower energy states of the adsorbed molecule.
Optical input may be provided by a monochromatic light source, such as one or more lasers. However, a non-monochromatic light source may be used if a light sensitive molecular species, such as rhodopsin, is attached as a polar group to or will otherwise form a chemical bond with the subject molecule to function as an input molecule therefore. In such case the electrons in the light sensitive input molecular species are excited by the light input, and this excitation is transferred to the subject molecule. This configuration makes more efficient use of the input light and permits amplification of the emitted optical signal. Using such light sensitive input device the invention may be characterized as an optical to optical valve, which may be considered analogous to other types of mechanical and electrical valves, the latter for example including electron tubes, transistors, other semi-conductor devices, and the like. Moreover, using such rhodopsin or other similar or dissimilar input and output devices may facilitate providing inputs to the subject molecules and obtaining useful outputs therefrom, for example without direct wire or fiber optics attachment, etc., thereto.
The invention may be characterized as a switch, an amplitude modulator, and/or an amplifier. As a switch the invention responds to an input to turn on or off a particular output, and this occurs at high speed, e.g. speeds on the order of 10−13 to 10−15 second. As an amplitude modulator the invention responds to an input to modulate the amplitude of an output, e.g. the intensity of light of a particular frequency, and this, too, can occur at the mentioned high speeds. As an amplifier the invention responds to an input, for example light, to produce an amplified output. The invention is described in detail with reference primarily to the producing of an optical output; however, the invention also may be used to produce electrical output. In one embodiment of the invention the adsorbed molecules are on an electrode surface. The electrode and molecules are placed in an electrolyte, such as a liquid bath. Illumination is by a monochromatic optical source, preferably a laser. Potential from an electrical source is applied to the adsorbed molecules between the electrode and the electrolyte, which serves as the other electrode.
In another embodiment the molecules are of the macrocyclic type, for example, phthalocyanines, porphyrines, chlorophyls, hemes, or cytochromes, that have characteristics of doped semi-conductor materials; and such molecules may be used with other semi-conductor materials, such as conventional doped materials. Such semi-conductor materials provide the needed potential application to the adsorbed molecules to cause the overall structure to have operational characteristics of, for example, a transistor. Such macrocyclics exhibit p type semi-conductor properties and also are photoactive. Therefore, for such transistor to be complete, the other material used at the opposite sides of the p type material should be n type semi-conductor material. Another solid state semi-conductor type device in which the invention may be used is a diode and it is contemplated that other type semi-conductor devices also may employ the invention. The semi-conductor devices according to the invention may be used in conventional ways, e.g. relying on transistor action for an amplifier or switch, etc. Still another solid state semi-conductor device in which the invention may be used is a field effect transistor (FET).